Cluster trinuclear

Alkyne-substituted transition metal clusters have been reviewed,122,123 and other reviews of interest have discussed cyclopentadienyl metal clusters of group 9 transition metals124 and hydrocarbyl ligand derivatives of group 6 through group 9 heterometallic clusters.125 

Triangular trinuclear systems in which the alkyne bridges two of the three metals have been prepared by reaction of preformed clusters with alkynes, as in Eq. (13),128 

Alkyne hydrido cluster complexes of the type [Co3(p.-H)2(/i-alkyne)Cp3] can be prepared by 1,2 double C—H activation of alkenes.132 133 For example, the p.-cycloalkyne complexes 36 can be prepared either from the respective cycloalkenes and [Co(C2H4)2Cp] or by using the reductive cleavage of cobaltocene with potassium as a source of CpCo fragments. (See Formula 36.) 

The bis(methyIidyne)hydridotricobalt cluster [Co3( U,-H)(ju,3-CH)2Cp3]+ reacts with carbon monoxide to form 37 by coupling of a HOC+ fragment with a cluster-bound methylidyne ligand.134 Carbon monoxide deinsertion and methylidyne-methylidyne coupling occur when 37 is treated with carbon monoxide under pressure to afford 38. (See Formulae 37 and 38.) 

The spin Hamiltonian of bilinear isotropic exchange for a trinuclear cluster adopts the form of 

The scalar product of the spin operators can be rewritten using the spherical irreducible tensor as follows 

Then the application of the Wigner-Eckart theorem yields 

The reduced matrix elements are evaluated for the tensor ranks according to the scheme 

Just this coupling scheme determines the -symbols which all collapse into 67-symbols owing to the presence of one zero element (Table 11.2). 

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Tungsten pentachlofide [13470-13-8], WCl, mp 243°C, bp 275.6°C, is a black, crystalline, deHquescent soHd. It is only slightly soluble in carbon disulfide and decomposes in water to the blue oxide, 200 2. Magnetic properties suggest that tungsten pentachlofide may contain trinuclear clusters in the soHd state, but this stmcture has not been defined. Tungsten pentachlofide may be prepared by the reduction of the hexachloride with red phosphoms (9). 

For trinuclear cluster complexes, open (chain) or closed (cycHc) stmctures are possible. Which cluster depends for the most part on the number of valence electrons, 50 in the former and 48 in the latter. The 48-valence electron complex Os2(CO)22 is observed in the cycHc stmcture (7). The molecule possesses a triangular arrangement of osmium atoms with four terminal CO ligands coordinated in a i j -octahedral array about each osmium atom. The molecule Ru (00) 2 is also cycHc and is isomorphous with the osmium analogue. 

A structurally characterized gold complex with a C5HPh4 ligand Au(r C5HPh4)(PPh3) (46a) was reported [66], An unusual trinuclear cluster 46b derived therefrom was also characterized by X-ray structural analysis. 

Three-membered metallocycles (trinuclear clusters). S. P. Gubin, Russ. Chem. Rev. (Engl. Transl.), 1985,54,305 (169). 

In addition, the reaction of the diruthenium complex [Ru2Cp 2S4] with [RhCp (MeCN)3](Pp6)2 has been reported to afford the trinuclear cluster [RhRu2Cp 3S4(MeCN)](PF6)2 in 85% yield (Scheme 66) [147],... 

With trinuclear clusters, we are now dealing with systems whose electronic structure depends on multiple intersite interactions that may differ from one iron pair to another. As a result, the separation between adjacent energy levels depends, not on the magnitude of these interactions, but on their difference. This may give rise to low-lying excited levels, which may have far-reaching effects on both the EPR spectrum and the relaxation properties. 

The trinuclear clusters Co3(//3-CR)(CO)9 are the most common precursors utilized in the very mixcd -metal exchange reactions reported thus far (Fig. 40),... 

Fig. 7.1 Idealized structures of the trinuclear cluster chalcogenides M3Q4L9 (type I, (a)) and M3Q7U (type II, (b)).

In organometallic systems in particular, clusters with bridging alkylthiolates are well known, as exemplified by Co2(Cp)2(/i-SCH3)2, which undergoes reactions with alkyne-cobalt complexes to yield trinuclear clusters.170... 

All of these trinuclear clusters are 42e and this is the most common electron count. However, a 46e cluster, [Pt3(/r-CO)(/r-dppm)4]2+ has been obtained by reacting [Pt3(/r-dppm)3(PPh3)] with CO.537 The Pt—Pt bond lengths (2.620-2.648 A) are remarkably similar to those in the 42e clusters.537... 

Mixed palladium/platinum analogues of these trinuclear clusters have also been reported. The first of these, [PtPd2Cl(PPh2)2(PPh3)3]+, was prepared by the reaction of [PdCl(PPh3)3]+ with [PtCl(PPh3)3]+.538... 

The photochemistry of Ru3(CO)y2 has been investigated in our laboratory (3-5) and others (6-11) and has been shown to involve both photofragmentation of the cluster (Equations 1 and 2) and photolabi-lization of carbonyls to give substituted trinuclear clusters Ru3(C0)] ] L (Equation 3). 

Ru3(CO)12(117)3] and [H4Ru4(CO)11(117)] as catalyst precursors in the hydrogenation of non-activated alkenes under biphasic conditions. Each cluster displays activity under moderate conditions, ca. 60 atm. H2 at 60 °C with catalytic turnovers up to ca. 500. The trinuclear clusters undergo transformations during reaction but can be used repeatedly without loss of activity.325... 

The trinuclear cluster [(/i-H)2Ru3(/i3-0)(C0)5(DPPM)2] is also an efficient catalyst for alkene hydrogenation reaction, for which Bergounhou proposed the catalytic Scheme 73.38... 

Figure lb, Representative trinuclear cluster species of the high- and low-valent... 

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